The present invention relates to an automatic conveying system of a car safety belt, more especially to an electronic control method of a car safety belt that controls various alarm functions and directions of a motor for releasing and fastening of the belt by using a microprocessor.
Generally, a car safety belt mounted on the seats is to be manually buckled for the safety of the driver and passenger, and the users of the belt, such as drivers and passengers, come to require a belt system with far more convenient functions.
For the relay-type control of the prior car safety belt as shown in FIG. 1, a starting switch SW1, a door switch SW2, a speed switch SW3, a backward switch SW4, a conveying position releasing switch SW5, a conveying position fastening switch SW6 and a lap belt buckle switch SW7 which are mounted in a car are electrically connected to a start sensing relay RY1, a door sensing relay RY2, a speed sensing relay RY3, a backward sensing relay RY4, a conveying position releasing relay RY5 and a conveying position fastening relay RY6 in the control unit 2 respectively, so that the determination of a rotational direction of the motor according to the operational state of the above relays causes the belt conveying system to move forward or backward (releasing position or fastening position) as well as to give the alarm through the alarm lamp L1 on malfunctioning.
In FIG. 1, the motor drive relay 3 is a conventional switch for control the operation of the motor. Switch 3 includes two single-pole, double-throw switches for connecting the B.sup.+ and ground connections to the motor under control of the control unit 2. With the switch contacts thrown as shown, both of the terminals of the motor are connected to ground and hence the motor is in the stationary, non-driven state. If control unit 2 causes one of the switch contacts to be thrown, then the motor will have the B.sup.+ voltage applied to one terminal of the motor while the other terminal of the motor remains connected to ground, hence driving the motor in a first direction. If the other of the switch contacts is thrown by operation of control unit 2 and the first contact remains as shown, then the B.sup.+ voltage will be applied to the other of the terminals of the motor leaving the first terminal connected to ground and hence the motor will be driven in the opposite direction. If both of the double-pole switch contacts of FIG. 3 are actuated by the control unit 2, then both terminals of the motor will be connected to the B.sup.+ voltage and hence the motor will be in the stationary, non-driven state. Switch 3 is a conventional motor control unit well known in existing car safety belt systems. However, the above relay-type control method of the safety belt has problems in that the necessity of relays corresponding to respective input signals makes cost high and the space occupied by them large, and in that life of the relays' electric contacts becomes shortened.
Another problem for the relay-type control method goes to a difficulty in checking when the connected peripherals are in trouble because each of the contacts of the relays are connected with each other in order for the motor of the travel system to perform simple functions such as stopping, a forward direction rotation and a reverse direction rotation.